Prior to recent neuroscience advances, Csikszentmihalyi’s flow theory was merely a phenomenologicaltheory based on qualitative interviews or self-report scales. Recent advancements in brain imaging and physiological measurement techniques provide details of the neurobiological underpinnings of flow.

The neuroanatomy of the brain as well as cognitive function evolved in a hierarchical fashion (Dietrich, 2003, 2004, 2006). It began with the development of the outermost area of the brain known as the cerebral cortex, particularly the pre-frontal cortex (Dietrich, 2003, 2004, 2006). The pre-frontal cortex increases cognitive and behavioral flexibility, which increased adaptability of the human species. The frontal cortex enables evolutionary adaptive capacities due to its ability for higher-cognitive function, including, but not limited to self-construct, self-reflective consciousness and cognitive flexibility, complex social function, and theory of mind (Dietrich, 2003, 2004, 2006). Despite the importance of these functions for long-term survival, they appear in direct contrast to the experience of a loss of self-awareness while in flow. Therefore, Dietrich (2003, 2004, 2006) suggested that flow occurs because of ‘transient hypo-frontality,’ a temporary suppression of prefrontal circuits.

Transient hypo-frontality theory (THT). Dietrich (2003, 2004a, 2006) described a down-regulation of activity in the prefrontal and conscious explicit brain during execution of well-learned skills (such as athletic skills). Sport activity creates a reliance on the cerebellar implicit motor and sensory regions of the brain (Sadlo, 2016). THT suggests that the brain down-regulates neural structures that are not necessary for the activity (Dietrich, 2003, 2004a, 2006). Dietrich (2009) suggested that the down-regulation of neural circuits progresses from brain areas supporting “the highest cognitive functions [of the pre-frontal cortex], down the functional hierarchy, one phenomenological subtraction at a time, to brain areas supporting the most basic ones” (p. 74). Dietrich (2009) posited that THT is based on well-researched principles of brain functioning: “(1) the brain has a finite energy supply; (2) that bodily motion is an extremely demanding task in computational terms - that is for the brain, not the body; and (3) that neural processing occurs on a competitive basis” (p. 73).

Due to the limited energy supply, the brain has limited resources (Dietrich, 2002). Dietrich (2003) proposed athletes may be particularly susceptible to transient hypo-frontality because “activation of motor and sensory systems during exercise comes at the expense of, first and foremost, the higher cognitive centers of the prefrontal cortex” (p. 240).The foundation of THT is that bodily motion forces the brain to make profound changes to the way it assigns metabolic resources (Dietrich, 2006). Information processing in the brain is competitive (Dietrich, 2006). Dietrich (2006) explained “because the brain cannot maintain activation in all neural structures at once, the activation of a given structure must come at the expense of others” (p. 80). When an individual experiences flow, Dietrich (2006) argued the brain experiences “a severe strain on the brain's limited information-processing capacity,” which “should result in a concomitant transient decrease in neural activity in structures that are not directly essential to the maintenance of the exercise” (p. 81).

Researchers refer to the explicit-implicit system as “conscious-unconscious, declarative-non-declarative, voluntary-automatic, or deliberate-spontaneous” (Dietrich, 2004a, p. 749). THT suggests that through skill repetition, individuals’ brains rely less on the explicit pre-frontal system and more on the implicit cerebellum and basal-ganglia (Sadlo, 2016). The process of building a skill in the implicit system is the act of “internalizing” or an action becoming “second nature” (Dietrich, 2004a, p. 750). The deactivation of the frontal cortex may benefit athletes as it suppresses a hyper-vigilante mind-state that overanalyzes internal experiences with respect to personal relevance (Dietrich, 2004a). THT results in a trade-off between the flexible pre-frontal system, in favor of the efficient implicit performance system (Dietrich, 2003, 2004a, 2006).

The theory of transient hypo-frontality explains what happens in the brains of athletes in flow—including the costs and benefits of efficient information processing in the implicit system. The flexibility/efficiency trade-off of transient hypo-frontality has advantages for athletic performance in flow activities; however, the suppression of the frontal cortex and flexible explicit system may impair other areas of life. For example, pre-frontal damage to the ventral medial (VM) region impairs social function (Dietrich, 2004a). As in the case of Phineas Gage, damage to the VM cortex results in “frontal syndrome” leading to “inappropriate social behaviors, lack of moral judgment, few social inhibitions, few abstract thought processes, an inability to plan for the future, and/or difficulty to maintain a plan of action” (Dietrich, 2004a, p. 1013). Without an active prefrontal cortex, athletes may lose the ability to inhibit inappropriate or maladaptive behaviors that place them at risk of the negative consequences associated with the dark side of flow (Dietrich, 2004a). Moreover, the brain structures not required for exercise (e.g., the amygdala, which is responsible for fear/threat detection), might fail during flow, which could explain increased risky behavior while in flow (Dietrich, 2004a).

The neurochemistry of flow. The positive consequences of flow may be due to alterations in neurotransmitter mechanisms such as dopamine (De Manzano, Cervenka, Jucaite, Hellenäs, Farde, & Ullén, 2013), endorphins (Hoffman, 1997), norepinephrine (Dishman, 1997), endocannabinoids (Dietrich & McDaniel, 2004; Sparling, Giuffrida, Piomelli, Rosskopf, & Dietrich, 2003; Tantimonaco, Ceci, Sabatini, Catani, Rossi, Gasperi, & Maccarrone, 2014), and serotonin (Chaouloff, 1997). Kotler (2014a) expanded on the impact of these neurochemicals, stating these are among the most addictive neurochemicals in the world. Further exploration of the neurochemistry of flow is beyond the scope of this project; however it will be further explored in future research.